PortletContext-aware subclass of PathMatchingResourcePatternResolver,
able to find matching resources below the web application root directory
via Portlet API's PortletContext.getResourcePaths.
Falls back to the superclass' file system checking for other resources.

The advantage of using PortletContext.getResourcePaths to
find matching files is that it will work in a WAR file which has not been
expanded too.

doFindPathMatchingFileResources

Overridden version which checks for PortletContextResource
and uses PortletContext.getResourcePaths to find
matching resources below the web application root directory.
In case of other resources, delegates to the superclass version.